FIG. 14 is a drawing of the constitution of a conventional multi-nozzle ink jet head. This head 10 shows an example of the application of bimorph actuators in which a diaphragm 102 and a piezo elements 101 are laminated together as driving elements. Regarding the method of producing this head, a plurality of individual electrodes 100 are formed by sputtering on an MgO substrate, not shown, and the piezos 101 are further laminated on to a thickness of a few μm, and pattern formation is carried out. After this, a metal (for example Cr) that will become the common electrode cum diaphragm 102 is formed to a few μm over the whole surface, thus forming the bimorph structures.
A pressure chamber forming member (dry film resist) 103 and a nozzle forming member 105, which are prepared separately, are then joined on, with positional alignment being carried out with the individual electrodes 100 of the bimorph structures. After that, the MgO substrate is removed by etching, thus completing the multi-nozzle head plate 10.
Regarding the operation of this head 10, ink is fed to the head 10 from an ink tank, not shown, and then within the head 10, the ink is fed through a common channel and ink supply channels to pressure chambers 104 and nozzles 106. Driving signals are applied to the individual electrodes (the electrodes corresponding to the respective nozzles) 100 from a driving circuit, whereupon, due to the piezoelectric effects of the piezo 101, the diaphragm 102 bends towards the inside of the pressure chamber 104 as shown by the dashed line in FIG. 14, and hence ink is ejected from the nozzle 106. The ink forms dots on a printing medium, thus forming a desired image.
Regarding the deformation during driving shown by the dashed line in FIG. 14, a strain force due to the piezoelectric effects of the piezo 101 (in particular the transverse effect orthogonal to the electric field) acts as a bending moment at the bending section neutral axis due to differences in the sectional shape (in particular the thickness) and the Young's modulus between the electrode 100, the piezo 101 and the diaphragm 102, and hence the bimorph structure which comprises the electrode 100, the piezo 101 and the diaphragm 102 as a whole bends.
To make this bending act so that the ink in the pressure chamber 104 flows, it is necessary to fix the bimorph structure to the pressure chamber 104. As a result, it becomes possible for the surface of the diaphragm 102, which bends with the fixed part as a reference position, to change the volume of the pressure chamber 104, whereupon ink is ejected.
As shown in the schematic drawing of FIG. 15, in the multi-nozzle ink jet head 10 in which the volume of the pressure chambers 104 is changed by bending of the diaphragm 102, if the density of the nozzles 106 is made high, then the walls 103 between the pressure chambers 104 communicating with adjacent nozzles 106 (the pressure chamber walls) become thin. That is, the fixing parts of the diaphragm 102 become narrow. For example, in a 150 dpi head, the nozzle spacing is about 169 μm, and hence it is necessary to make the thickness of the pressure chamber walls 103 35 μm.
This reduces the rigidity of the fixing parts 103 of the diaphragm 102, and hence the fixing parts 103 no longer function sufficiently as fixed ends of the diaphragm 102. As a result, in the case of a structure in which adjacent pressure chambers 104 are covered by the same diaphragm 102, when a single part of the diaphragm bends (single-element driving), the part of the diaphragm for the adjacent element is pulled in in the direction A of the bending, i.e. it is difficult for local bending of only the driven part to occur. Moreover, as shown in FIG. 15, when various parts of the diaphragm 102, including the parts at adjacent elements, bend together (multi-element driving), the parts of the diaphragm 102 on either side of the fixing part 103 pull against one another in the directions of the arrows A and B, and the two pulls balance one another, and hence it is easy for local bending of only the driven parts to occur.
In this way, mechanical driving interference (cross talk) occurs in which the bending of the diaphragm 102 differs according to the driving state (single-element driving or multi-element driving). In the ink jet head, this manifests itself as fluctuations in the ink flight characteristics, resulting in a drop in printing quality.
Moreover, a technique is known for dividing a single diaphragm 102 into parts for each of the pressure chambers 104, but with thin pressure chamber walls 103, it is very difficult to secure the reliability of the diaphragm fixing parts (the structure that functions as fixed ends for the diaphragm and also seals the pressure chambers) if the nozzle density is high. Moreover, even if the diaphragm is divided, the strain energy that the piezos 101 exert on the fixed ends of the diaphragm 102 will not change, and hence the energy transmitted to adjacent elements via the pressure chamber walls 103 will not change. As a result, in a high-density head in which the pressure chamber walls are thin, dividing the diaphragm is not an effective measure for solving the problem, and cross talk cannot be prevented.